9 ms·

Germany's inefficient love affair with open windows (2021)

25 points by KennyBlanken 3y ago

6R1M0R4CL3 3y ago
germans have the best engineers in the world and are the most clever people i have ever met. if they do something like aerating their homes, i will bet they are, again, more clever than us who don't do it as much... indoor pollution is something we don't detect and suffer, and again germans beat us there.
KolmogorovComp 3y ago
The article cites windows opening inward as a reason for inefficient ventilation, yet the answer is to… insulate less? > The key may be to have less insulation, because the current system seems to be too airtight to accomodate for residents' differing preferences Why not change the windows to open outward/upward?
- rad_gruchalski 3y ago
  The point is: you open those windows to let the humidity out. Warm air holds more water than cold air. The warmer it gets inside, the more humidity. If you don’t open your windows, the humidity escapes through least isolated areas, very often window sills. Sills get naturally colder, at below 12 degrees celsius you get mold in the sills. So, open your windows to blow the humidity out of the apartment but don’t open for too long so the sills don’t cool down too much, especially not below 12 degrees celsius.
  - rawgabbit 3y ago
    Is there a modern type of window or device that will prevent mold, without requiring periodically opening the window?
    - blacksmith_tb 3y ago
      Yes, the device is a Heat Recovery Ventilator[1]. As you increase the insulation and airtightness of the windows to conserve energy, you need to bring fresh air in steadily (and pump air out). The HRV handles that, and passes the incoming air through a heat exchanger with the outgoing air, which is useful whether you're trying to keep warm air inside (in the winter) or cool air inside (in the summer. 1: https://en.wikipedia.org/wiki/Heat_recovery_ventilation https://en.wikipedia.org/wiki/Heat_recovery_ventilation
      - rawgabbit 3y ago
        Thank you for the link.
- lxgr 3y ago
  > the answer is to… insulate less? Yeah, that's an absurd suggestion. Insulation against heat transfer and insulation against mass transfer are also two different things. Although in a trivial setup the latter inevitably leads to the former, that doesn't need to be the case: Counterflow heat exchangers are a thing. > Why not change the windows to open outward/upward? Opening outward is much harder to handle (as it requires something to pull the window back in to close it); upward would need a robust mechanism that prevents the window from violently smashing down due to gravity. Sliding windows have neither downside, but are much, much worse at noise and thermal insulation.
mtmail 3y ago
Related and currently on the frontpage with 80 comments: "Stoßlüften: Shock Ventilation" "This word (and concept) is especially found in public places and schools all around Germany." https://news.ycombinator.com/item?id=38813856 https://news.ycombinator.com/item?id=38813856
hasoleju 3y ago
Based on the title I first thought there is an open source operating system used in Germany I was not aware of. But is really true „Lüften“ is something we do in every room every morning here. Luckily modern Bauhaus architecture style homes have windows down to the floor so that opening them is always possible because there is no sideboard with plants on top in front of the window.
Slartie 3y ago
It is actually kind of common in Germany that landlords attach copies of news articles about the need for correct ventilation or similar "notes" to rental contracts when handing them over to a new resident. Not exactly part of the rental contract (because it's not legally possible to dictate the exact ventilation cycle desires of the landlord in a rental contract), but still a very clear hint at what's expected of you. I've never assumed anyone to actually do all of this excess ventilation, though...I've always been too lazy to "open all windows three times a day for five minutes each" (where the heck do people find the time to do that each and every day?), and the "solution" of just opening the window a little over a long period is so obviously expensive in terms of heating costs that I rather keep most windows closed most of the time (except bathroom after showers for obvious reasons).
- lm28469 3y ago
  The average person spends like 3-5 hours in front of a screen for entertainment only, I'm fairly sure spending 30s here and there to open windows is in the realm of possibilities
  - kaashif 3y ago
    Average person spends 3-5 hours in front of a screen, so this task taking less than 3 hours is reasonable to do. Something about that rubs me the wrong way. Doesn't it matter that the task is menial and doesn't seem all that effectual?
    - imtringued 3y ago
      It's actually quite meaningless. Yes, water vapor in the air causes mold, but here is the thing: the water only sticks to cold walls. It is the combination of a cold wall plus water in the air that is the problem. Ventilation alone cannot make your wall warmer, in fact, excessive ventilation may cool your walls down even faster. As expensive as it might sound, the only reliable solution is to properly insulate the wall and keep it warm.
      - 3y ago
PreInternet01 3y ago
OK, although "stupid Germans keep opening windows to defeat stupid green goals" is of course a take, in reality, a modern energy-efficient Euro-style building will: -Indeed be 'airtight', in the sense that limited air (and noise, as a bonus) will enter or leave the building except via defined ventilation routes. -Offer primary 24/7 ventilation (mostly for CO2 management) via ingress/egress vents as part of a balanced ventilation system, which performs 'comfort' regulation of incoming air temperature using heat recovered from outgoing air. -Heat or cool the building via under-floor convection connected to a reversible heat pump. This will slowly but surely bring most of the building mass to a comfortable temperature regardless of season. -In addition to basic ventilation and heating/cooling offer very-well-insulated yet securely operable windows for additional temporary ventilation. Window openings are very much defined ventilation routes as part of the 'airtight' plan. The important things to keep in mind here are that the balanced ventilation system prevents things like mold already, and that opening windows for brief periods of time (as in: measured in hours) for (perceived) comfort won't impact energy efficiency very much at all. The most relevant criticism here is that retrofitting existing buildings for the above scheme is a significant challenge, but that doesn't quite seem to be the point the article wants to be making...
RGamma 3y ago
I highly recommend installing a decentralized ventilation system with enthalpy exchanger in often used rooms like the sleeping room. It's super efficient and improves air quality a lot when your building is highly insulated. The enthalpy part is important because winter air is pretty dry after heat exchange. Bonus points when you can fit good air filters (ePM1 50%+). Also, some systems offer a summer bypass for cooling in summer without AC as well as "smart functions" like orchestration of multiple devices or automatic control via CO2/humidity sensor. Central ventilation is unfortunately very hard to retrofit...
- amluto 3y ago
  > ePM1 50%+ If there’s actual poor air quality (smoke, etc), this is inadequate. 50% is fine for a recirculating system — fine particles will be reduced by half on each pass. For for a single pass system, if you have 50 μg/m3 outdoors (quite common in a lot of places, sadly) you get 25 μg/m3 coming in through your fancy ventilation system, which is not great. What you want is a great honking filter, 95% or better, with a prefilter. You’ll pay several hundred dollars for that big filter, but you’ll be running it at low velocity (maybe 150cfm of flow in a 24”x24” filter housing), so it will have minimal pressure drop and will last a long time. Even an actual HEPA filter wouldn’t be out of place here. But even the really fancy European ERV/HRV brands use those inadequate ePM1 50% filters. I’ve even measured them with a handheld particle counter — they work every bit as poorly as one would expect from the specs. And those filters are small, and they gunk up quickly.
  - bradknowles 3y ago
    The thing about HRV/ERV filters is that it is effectively a pre-filter, because the real filtering is supposed to be done by the HVAC system that the HRV/ERV dumps into. You still get your HEPA filtering, because that's on your HVAC system.
  - RGamma 3y ago
    Yeah, it's far from optimal, sadly. The best I found for my device were (allegedly) ePM1 70%. We get quite a lot of smoke exposure from badly behaved fireplaces/unsuitable (palette) wood right now and it reeks. Got any suggestions how I could retrofit a better filter solution for my device (Zehnder ComfoSpot50). It has "slotted" filters like these https://cleanfilter.eu/en/product/zehnder-comfospot-50-filters/?v=3a52f3c22ed6 https://cleanfilter.eu/en/product/zehnder-comfospot-50-filte.... Maybe something to chain outside in front of the intake or inside after the outlet (though I'm afraid I could run the Comfospot out of specs..)? Or I guess I could kind of suboptimally get a standalone one. These handheld particle counters look intriguing. Unfortunately a bit on the expensive side... Maybe I can borrow one, might give me some hard data for contacting my municipality about this.
MarkusWandel 3y ago
But you don't understand! It's simply impossible to sleep in a room without an open window! Every German visitor has insisted on this. I was born in Germany myself,and of course slept with the window open, that's just what one did. But have long ago come to the land of heating and air conditioning, sometimes both on the same day, and HEPA filtration, God forbid that dirty, unsanitary nature might make inroads in your germ-free sanctum. The irony is that the windows that Germans insist on leaving open at night put our crank casement things to shame. Double gasketed? No, triple gasketed! Guaranteed airtight to god-knows-how-many psi, and without even a center post. And open horizontally or tilt vertically depending on which way you turn the handle.
- db48x 3y ago
  They’re not exactly limited to Germany, although sash windows are more popular here. If you want them, just go to a nearby home improvement store and buy them. Search for “Tilt and Turn” casement windows.
_aavaa_ 3y ago
Not one mention of a heat recovery system. You can have your house very airtight and still be able to turn the air over without loosing as much energy in the air.
wrp 3y ago
Related to leaving windows open...My friend went to Germany for work last summer and was housed in a new apartment. While she mostly enjoyed it, she complained a lot about the lack of screens on windows to keep out the fruit flies. That could be one reason for not wanting to leave your windows open.

25 points by KennyBlanken 3y ago

germans have the best engineers in the world and are the most clever people i have ever met. if they do something like aerating their homes, i will bet they are, again, more clever than us who don't do it as much... indoor pollution is something we don't detect and suffer, and again germans beat us there.

KolmogorovComp 3y ago

The article cites windows opening inward as a reason for inefficient ventilation, yet the answer is to… insulate less? > The key may be to have less insulation, because the current system seems to be too airtight to accomodate for residents' differing preferences Why not change the windows to open outward/upward?

rad_gruchalski 3y ago
The point is: you open those windows to let the humidity out. Warm air holds more water than cold air. The warmer it gets inside, the more humidity. If you don’t open your windows, the humidity escapes through least isolated areas, very often window sills. Sills get naturally colder, at below 12 degrees celsius you get mold in the sills. So, open your windows to blow the humidity out of the apartment but don’t open for too long so the sills don’t cool down too much, especially not below 12 degrees celsius.
- rawgabbit 3y ago
  Is there a modern type of window or device that will prevent mold, without requiring periodically opening the window?
  - blacksmith_tb 3y ago
    Yes, the device is a Heat Recovery Ventilator[1]. As you increase the insulation and airtightness of the windows to conserve energy, you need to bring fresh air in steadily (and pump air out). The HRV handles that, and passes the incoming air through a heat exchanger with the outgoing air, which is useful whether you're trying to keep warm air inside (in the winter) or cool air inside (in the summer. 1: https://en.wikipedia.org/wiki/Heat_recovery_ventilation https://en.wikipedia.org/wiki/Heat_recovery_ventilation
    - rawgabbit 3y ago
      Thank you for the link.
lxgr 3y ago
> the answer is to… insulate less? Yeah, that's an absurd suggestion. Insulation against heat transfer and insulation against mass transfer are also two different things. Although in a trivial setup the latter inevitably leads to the former, that doesn't need to be the case: Counterflow heat exchangers are a thing. > Why not change the windows to open outward/upward? Opening outward is much harder to handle (as it requires something to pull the window back in to close it); upward would need a robust mechanism that prevents the window from violently smashing down due to gravity. Sliding windows have neither downside, but are much, much worse at noise and thermal insulation.

mtmail 3y ago

Related and currently on the frontpage with 80 comments: "Stoßlüften: Shock Ventilation" "This word (and concept) is especially found in public places and schools all around Germany." https://news.ycombinator.com/item?id=38813856 https://news.ycombinator.com/item?id=38813856

hasoleju 3y ago

Based on the title I first thought there is an open source operating system used in Germany I was not aware of. But is really true „Lüften“ is something we do in every room every morning here. Luckily modern Bauhaus architecture style homes have windows down to the floor so that opening them is always possible because there is no sideboard with plants on top in front of the window.

Slartie 3y ago

It is actually kind of common in Germany that landlords attach copies of news articles about the need for correct ventilation or similar "notes" to rental contracts when handing them over to a new resident. Not exactly part of the rental contract (because it's not legally possible to dictate the exact ventilation cycle desires of the landlord in a rental contract), but still a very clear hint at what's expected of you. I've never assumed anyone to actually do all of this excess ventilation, though...I've always been too lazy to "open all windows three times a day for five minutes each" (where the heck do people find the time to do that each and every day?), and the "solution" of just opening the window a little over a long period is so obviously expensive in terms of heating costs that I rather keep most windows closed most of the time (except bathroom after showers for obvious reasons).

lm28469 3y ago
The average person spends like 3-5 hours in front of a screen for entertainment only, I'm fairly sure spending 30s here and there to open windows is in the realm of possibilities
- kaashif 3y ago
  Average person spends 3-5 hours in front of a screen, so this task taking less than 3 hours is reasonable to do. Something about that rubs me the wrong way. Doesn't it matter that the task is menial and doesn't seem all that effectual?
  - imtringued 3y ago
    It's actually quite meaningless. Yes, water vapor in the air causes mold, but here is the thing: the water only sticks to cold walls. It is the combination of a cold wall plus water in the air that is the problem. Ventilation alone cannot make your wall warmer, in fact, excessive ventilation may cool your walls down even faster. As expensive as it might sound, the only reliable solution is to properly insulate the wall and keep it warm.
    - 3y ago

PreInternet01 3y ago

OK, although "stupid Germans keep opening windows to defeat stupid green goals" is of course a take, in reality, a modern energy-efficient Euro-style building will: -Indeed be 'airtight', in the sense that limited air (and noise, as a bonus) will enter or leave the building except via defined ventilation routes. -Offer primary 24/7 ventilation (mostly for CO2 management) via ingress/egress vents as part of a balanced ventilation system, which performs 'comfort' regulation of incoming air temperature using heat recovered from outgoing air. -Heat or cool the building via under-floor convection connected to a reversible heat pump. This will slowly but surely bring most of the building mass to a comfortable temperature regardless of season. -In addition to basic ventilation and heating/cooling offer very-well-insulated yet securely operable windows for additional temporary ventilation. Window openings are very much defined ventilation routes as part of the 'airtight' plan. The important things to keep in mind here are that the balanced ventilation system prevents things like mold already, and that opening windows for brief periods of time (as in: measured in hours) for (perceived) comfort won't impact energy efficiency very much at all. The most relevant criticism here is that retrofitting existing buildings for the above scheme is a significant challenge, but that doesn't quite seem to be the point the article wants to be making...

RGamma 3y ago

I highly recommend installing a decentralized ventilation system with enthalpy exchanger in often used rooms like the sleeping room. It's super efficient and improves air quality a lot when your building is highly insulated. The enthalpy part is important because winter air is pretty dry after heat exchange. Bonus points when you can fit good air filters (ePM1 50%+). Also, some systems offer a summer bypass for cooling in summer without AC as well as "smart functions" like orchestration of multiple devices or automatic control via CO2/humidity sensor. Central ventilation is unfortunately very hard to retrofit...

amluto 3y ago
> ePM1 50%+ If there’s actual poor air quality (smoke, etc), this is inadequate. 50% is fine for a recirculating system — fine particles will be reduced by half on each pass. For for a single pass system, if you have 50 μg/m3 outdoors (quite common in a lot of places, sadly) you get 25 μg/m3 coming in through your fancy ventilation system, which is not great. What you want is a great honking filter, 95% or better, with a prefilter. You’ll pay several hundred dollars for that big filter, but you’ll be running it at low velocity (maybe 150cfm of flow in a 24”x24” filter housing), so it will have minimal pressure drop and will last a long time. Even an actual HEPA filter wouldn’t be out of place here. But even the really fancy European ERV/HRV brands use those inadequate ePM1 50% filters. I’ve even measured them with a handheld particle counter — they work every bit as poorly as one would expect from the specs. And those filters are small, and they gunk up quickly.
- bradknowles 3y ago
  The thing about HRV/ERV filters is that it is effectively a pre-filter, because the real filtering is supposed to be done by the HVAC system that the HRV/ERV dumps into. You still get your HEPA filtering, because that's on your HVAC system.
- RGamma 3y ago
  Yeah, it's far from optimal, sadly. The best I found for my device were (allegedly) ePM1 70%. We get quite a lot of smoke exposure from badly behaved fireplaces/unsuitable (palette) wood right now and it reeks. Got any suggestions how I could retrofit a better filter solution for my device (Zehnder ComfoSpot50). It has "slotted" filters like these https://cleanfilter.eu/en/product/zehnder-comfospot-50-filters/?v=3a52f3c22ed6 https://cleanfilter.eu/en/product/zehnder-comfospot-50-filte.... Maybe something to chain outside in front of the intake or inside after the outlet (though I'm afraid I could run the Comfospot out of specs..)? Or I guess I could kind of suboptimally get a standalone one. These handheld particle counters look intriguing. Unfortunately a bit on the expensive side... Maybe I can borrow one, might give me some hard data for contacting my municipality about this.

MarkusWandel 3y ago

But you don't understand! It's simply impossible to sleep in a room without an open window! Every German visitor has insisted on this. I was born in Germany myself,and of course slept with the window open, that's just what one did. But have long ago come to the land of heating and air conditioning, sometimes both on the same day, and HEPA filtration, God forbid that dirty, unsanitary nature might make inroads in your germ-free sanctum. The irony is that the windows that Germans insist on leaving open at night put our crank casement things to shame. Double gasketed? No, triple gasketed! Guaranteed airtight to god-knows-how-many psi, and without even a center post. And open horizontally or tilt vertically depending on which way you turn the handle.

db48x 3y ago
They’re not exactly limited to Germany, although sash windows are more popular here. If you want them, just go to a nearby home improvement store and buy them. Search for “Tilt and Turn” casement windows.

_aavaa_ 3y ago

Not one mention of a heat recovery system. You can have your house very airtight and still be able to turn the air over without loosing as much energy in the air.

wrp 3y ago

Related to leaving windows open...My friend went to Germany for work last summer and was housed in a new apartment. While she mostly enjoyed it, she complained a lot about the lack of screens on windows to keep out the fruit flies. That could be one reason for not wanting to leave your windows open.